docs: 更新 README feature 表 + 升级指南 + 示例注释 + roadmap 同步

- README 添加 feature 组合表 + 模块级 features 清单 + 升级指南
- 18 个 example 顶部添加 Required features 注释
- roadmap.md 和 roadmap-v0.3.2.md 同步 Phase 26-27 完成状态
- cargo fmt 全量格式化（修复预存格式问题，CI format job 可通过）

src/engine/switch.rs

@@ -129,8 +129,7 @@ mod tests {
     }
 
     async fn make_manager_and_bundle() -> (Arc<SessionManager>, Arc<RuntimeBundle>) {
-        let store: Arc<dyn crate::memory::store::MemoryStore> =
-            Arc::new(InMemoryStore::new());
+        let store: Arc<dyn crate::memory::store::MemoryStore> = Arc::new(InMemoryStore::new());
         let provider = Arc::new(MockProvider::new(vec![
             assistant_text("response1"),
             assistant_text("response2"),
@@ -175,10 +174,7 @@ mod tests {
         {
             let session = sm.get(&sid).await.unwrap();
             let mut guard = session.lock().await;
-            guard
-                .set_session_data("key1", "value1")
-                .await
-                .unwrap();
+            guard.set_session_data("key1", "value1").await.unwrap();
         }
         sm.submit_turn(&sid, "hello").await.unwrap();